Ceramic articles (especially dense ceramic articles) are typically formed from a starting ceramic powder. The ceramic powder is formed into a shape using some suitable molding technique. The shape is then treated to form the desired ceramic article. For dense ceramic articles, such treatment includes a heat treatment to densify the shape.
Ceramic powders by themselves are generally unsuitable for molding into shapes because they have insufficient cohesive strength. Accordingly, binders and other molding aids are often combined with the ceramic powder (prior to molding) to facilitate molding of the powder as well as to add strength to the molded shape. The binders and/or molding aids are then removed in a later processing step usually involving heating to cause reaction and/or volatilization of those materials.
Goals of the molding step are to produce a molded shape which precisely conforms with the shape of the mold and to do so as reliably and inexpensively as possible. The molded shape should have sharp corners if the mold is designed to produce sharp corners. The shape should also be smooth and substantially free of cracks and tears.
For silicon nitride powders, the usual molding techniques are injection molding or hot extrusion. These processes are quite expensive (often requiring elevated temperatures and/or elaborate equipment) and require the use of relatively large amounts of organic binders and molding aids. Additionally, the large amount of these binders and aids often difficult to completely remove from the molded shape. Accordingly, there is need for improved molding methods and mixtures for molding.